This invention relates to continuous casting apparatus for continuously casting molten metal, and more particularly to continuous casting apparatus suitable for manufacturing a thin and broad cast piece and capable of high-speed casting.
In recent years, in the field of continuous casting, it has been requested to make the casting speed high. In particular, it has been strongly desired to establish a technology for producing a broad cast piece at high speed to the utmost from molten steel which is difficult to be cooled and whose solidification speed is low. When it can be realized, the matching with the processing capabilities before and behind the casting apparatus becomes possible. This is remarkably effective, not only in reduction in the cost of equipment, the cost of maintenance etc., but also in an enhancement in the productivity, and so on.
In establishing the high-speed continuous casting technology, there are several serious hindrances. The first hindrance is the production of a solidified shell in the casting process and its attendant problems. Since the cooling time of th cast piece decreases in proportion to the raised speed, the solidified shell inevitably becomes thin. On the other hand, when the mold is made long in order to secure a sufficient cooling time, an increase in the frictional resistance with the mold and an increase in bulging as are attributed to the static pressure of the molten metal are incurred. Anyway, the high-speed casting is extremely difficult due to the limitation in strength being the rupture of the solidified shell. Needless to say, the rupture of the solidified shell makes it unavoidable to stop the casting job, and moreover, it induces an explosion accident ascribable to the contact with cooling water. It must therefore be avoided by all means. In this manner, indispensable conditions for the high-speed casting are (a) that the thickness of the solidified shell can be sufficiently secured, (b) that the frictional resistance with the mold is low, (c) that the mold can sufficiently hold the static pressure of the molten metal, etc. The second problem is a restriction which comes from the scale of casting facilities, especially the height of a building. Increases in the size of equipment and the height of the building attendant upon the raised speed form a serious hindrance in practical use.
As continuous casting apparatuses for metals, various types have hitherto been proposed. A typical example put into practical use is, as shown in U.S. Pat. No. 3,659,643, a type wherein a cast piece cooled and mold within a vibrating molded is drawn out from outside while overcoming the frictional resistance with the mold. With the continuous casting apparatus of this type, however, it is difficult to raise the speed above the present speed (2 to 3 meter/min.) on account of the restriction on the strength of the solidified shell, etc.
Synchronous continuous casting apparatuses in which a mold having wall surfaces adapted to move in synchronoism with a cast piece as means for reducing the frinctional resistance with the mold have already been proposed in various forms. In, for example, the so-called Hazelett type continuous casting apparatus wherein a mold is formed of two sets of upper and lower movable parallel belts on long latus sides of a cast piece and caterpillars on short latus sides of the cast piece, molten metal pours into the caterpillars. This often causes the rupture of a solidified shell, and involves the danger of explosion due to the leakage of the molten metal. Another serious drawback is that on account of the lowering of rigidity etc. ascribable to the temperature rise of the upper and lower parallel belts arranged rectilinearly, the belts wave to render the casting impossible. At the present time, such the type of the continuous casting apparatus is put in practical use only in the field of non-ferrous metals which are easily quenched. As synchronous continuous casting apparatus similar to the aforecited type, there has also been proposed a type wherein a mold is constructed by vertically arranging movable belts or caterpillars. With this construction, however, it is very difficult to sufficiently hold the static pressure of molten metal. Likewise to the above, there is the disadvantage that the molten metal pours into the belts or the caterpillars, so a safe casting operation cannot be performed. Moreover, on account of the vertical mold system, the building becomes high to incur an increase in the cost of equipment, and it is difficult to achieve a high speed.